Contents

Variometer

The variometer signal is simply the derivative of the barometer signal. It gives a much more accurate vertical speed signal than is possible with GPS.This kind of measurement is used by the free flying community (hanggliding, paragliding, ballooning). A device that allows teams of pilots to share position and speed (with accurate vertical speed) data would be lots of fun.
Variometer Reference

Hardware

It could be best to filter and differentiate the analog pressure signal and then digitize. Another possibility is to differentiate the height in software. A robust solution is to compute a linear regression of a sliding window of height samples. The height samples can be computed using integer arithmetic by a pressure->altitude lookup table followed by interpolation. Maybe it's even possible to add detail based on the accelerometers.

These values are provided to listeners in multiple applications.
The sample rate should be application adjustable to conserve power.

Application code

Applications can use the altitude data or combine the data with GPS and accelerometer data.
Commonly Kalman filter/observer techniques are used to combine data from multiple sensor types into a robust(with respect to sensor noise), high accuracy estimate of position and speed in 3 axis.

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Variometer

The variometer signal is simply the derivative of the barometer signal. It gives a much more accurate vertical speed signal than is possible with GPS.This kind of measurement is used by the free flying community (hanggliding, paragliding, ballooning). A device that allows teams of pilots to share position and speed (with accurate vertical speed) data would be lots of fun.
Variometer Reference

Hardware

It could be best to filter and differentiate the analog pressure signal and then digitize. Another possibility is to differentiate the height in software. A robust solution is to compute a linear regression of a sliding window of height samples. The height samples can be computed using integer arithmetic by a pressure->altitude lookup table followed by interpolation. Maybe it's even possible to add detail based on the accelerometers.

These values are provided to listeners in multiple applications.
The sample rate should be application adjustable to conserve power.

Application code

Applications can use the altitude data or combine the data with GPS and accelerometer data.
Commonly Kalman filter/observer techniques are used to combine data from multiple sensor types into a robust(with respect to sensor noise), high accuracy estimate of position and speed in 3 axis.